1. Field of the Invention
The present invention relates to a magnetic pump in which an internal magnet is driven from the outside of the housing in order to cause the rotation of an impeller, and more particularly relates to improving the durability of the outer magnet of the pump.
2. Description of the Related Art
Conventionally, magnetic pumps have been widely used as engine cooling devices or lubricating devices in automobiles, motorcycles and the like. Generally, a magnetic pump has a magnetic coupling structure which is used to cause rotation of the impeller inside the pump housing. In such a magnetic coupling structure, the inner magnet of the impeller on which the inner magnet is mounted receives the magnetic force of an outer magnet which is appropriately disposed on the outside of the pump housing, so that this inner magnet is caused to rotate at a high speed as a result of the high-speed rotation of the outer magnet, thus causing the impeller to rotate.
In particular, in the case of magnetic pumps of the type in which [i] the inner magnet mounted on the impeller has a cylindrical shape, [ii] the outer magnet has a cylindrical shape, [iii] a cylindrical accommodating portion is formed in the pump housing, [iv] the inner magnet of the impeller is accommodated in said cylindrical accommodating portion, and [v] the outside surface of the abovementioned cylindrical accommodating portion is accommodated on the inner circumferential side of the cylindrical outer magnet, the area of the magnetic force exerted by the outer magnet on the inner magnet can be greatly increased, so that a magnetic pump which has a more powerful magnetic coupling can be obtained. The outer magnet is mounted on a holder, and said holder receives a rotational force from another driving source such as, for example, an engine, and rotates as a unit with the outer magnet.
A magnetic pump of this type is disclosed in Japanese Utility Model Laid-Open Application No. 3-32196. In this magnetic pump, the outer magnet is first of all devised as follows: specifically, a coupling main body made of a steel plate is fastened to the end portion (with respect to the axial direction) of the drive shaft. Groove-form engaging portions are formed in portions of a permanent magnet which is accommodated inside said coupling main body, and engaging portions which are formed by the buckling of portions of the coupling main body into said groove-form engaging portions are engaged with said groove-form engaging portions so that the coupling main body and permanent magnet are integrally fastened in the rotational direction and axial direction.
The outer circumferential side of the permanent magnet accommodated inside the coupling main body is covered and held by a coupling made of a steel plate, and is thus fastened in the rotational direction and axial direction. Accordingly, no problems arise in an ordinary environment. However, magnetic pumps are widely used as cooling water supply means or lubricating oil supply means in the engines of automobiles, motorcycles and the like, and in cases where such magnetic pumps are installed and used in engines, the use environment involves exposure to temperature changes or large temperature differences, such as when the temperature abruptly varies from a low temperature to a high temperature when the engine is started. Furthermore, such magnetic pumps are used under various harsh conditions such as severe vibration from the engine, vehicle body or the like.
The outer magnet and inner magnet constituting the magnetic coupling are generally made of brittle materials. Furthermore, magnets of this type are constantly used in the harsh environment described above.
As a result, the outer magnet in particular is subjected to the effects of abrupt temperature changes and severe vibration, and as a result of a synergistic effect of such conditions, there is a danger that looseness of the outer magnet may occur. Moreover, if the outer magnet should come loose from the magnet cup body, this results in a deterioration in the function of the pump.
Especially in the case of the outer magnet of the magnetic coupling which is thus exposed to a harsh environment, it is necessary to take countermeasures to prevent the abovementioned deterioration in function in cases where the magnetic pump is used in practical applications in engines or the like. An object of the present invention is to improve pump performance by preventing the separation of the outer magnet from the magnet cup body in harsh environments, such as the interiors of engines or the like.
Accordingly, the present inventor conducted diligent research in order to solve the above-mentioned problems. As a result, the inventor successfully prevented separation of the outer magnet from the magnet cup body even in cases where looseness was generated in the outer magnet, by constructing the present invention as a magnetic pump having a magnetic coupling structure in which an inner magnet disposed on an impeller is accommodated in a cylindrical accommodating portion of the housing, the outer circumferential surface of the accommodating portion is loosely inserted into the inner circumferential surface of a cylindrical outer magnet which is supported on its outer circumferential surface by a magnet cup body, and which rotates together with the magnet cup body, and the impeller rotates in accordance with the rotation of the outer magnet, wherein a cylindrical covering member which covers the inner circumferential surface of the outer magnet is mounted on the outer magnet.